The present invention relates to a method for manufacturing a gas mask canister which is worn by workers handling toxic gases in general industry, or which is used for protecting humans from toxic gases and particulates. More specifically, the present invention relates to a method for manufacturing a canister of gas mask, in which the manufacture is easy. Simple separating plates are installed within the canister so as to inhibit an overload in a high efficiency particulate air (HEPA) filter and to prevent leakage. The casing of the canister and the impregnated activated carbon particles filled therein can be reused. The radioactive materials contaminating on the outer surface of the canister can be easily removed.
In order to protect the workers in general industry using toxic gases, or to protect human lives from military toxic gases, gas masks are used in which impregnated activated carbon and a HEPA filter are provided. Actually, gas masks have been manufactured in various forms since the First World War as a means to protect against chemical military weapons. The gas masks were filled with impregnated activated carbon for removing toxic gases. The impregnated activated carbon consisted of activated carbon particles impregnated with oxides of: 5-9% of copper, 2-4% of chrome, 1-2% of zinc and 0.1-0.4% of silver. However, recently, those oxides, (particularly chrome) which are harmful to the human body are excluded. The remaining metal oxides are impregnated into the activated carbon, and impregnation with an amount of 4% TEDA (tri-ethyldiamine) follows. Various other impregnated materials are used in the gas masks. Domestically, gas masks which had been developed by the United States were introduced and used. At present, gas masks which make it possible to drink water and talk while wearing them have been developed and are supplied to soldiers. Besides the military use, masks have been developed for aeronautic use, civil defense use, industrial use, and radiological use (in the nuclear power plants).
Each gas mask includes a face portion, a canister, and a carrying sack. The canister is filled with impregnated activated carbon particles for removing toxic gases and a filter media for removing particulates. The canister removes the fine particulates and toxic gases to protect the wearer.
In the gas masks which are used in nuclear power plants, the mask can be reused by repeatedly cleaning the outer surface of the case which has been contaminated with radioactive materials until the gas mask shows a lowered performance. When the canister shows a lowered performance, the canister is classified as a radioactive waste requiring proper disposal. This radioactive waste requires a high disposal cost, and an economic loss is brought about. Therefore, if the impregnated activated carbon particles and the casing of the canister are reused, then the volume of the radioactive waste can be reduced to a great degree.
Generally, the canister of the gas mask includes a pre-filter, a HEPA filter, and an impregnated activated carbon particle layer.
The pre-filter removes coarse particulates to protect the activated carbon and the HEPA filter so as to extend the lifetime of the gas mask.
Besides the use of the impregnated activated carbon in the gas masks, the impregnated activated carbon is widely used in adsorption apparatuses for removing toxic gases in the chemical industries, for adsorbing organic iodides in nuclear power plants, and for purifying air from general industry facilities. Particularly, among the gaseous radioactive materials generated from nuclear power plants, the radioactive organic iodides are absorbed and removed by the KI (potassium iodide), TEDA (tri-ethylene diamine) impregnated activated carbon.
The HEPA filter shows a removing efficiency of 99.9% for the particulates of 0.001 .mu.m to several .mu.m. Even for the DOP aerosol of 0.3 .mu.m which is the maximum penetrating size, the minimum efficiency should be 99.97%. The HEPA filter is installed within the canister, to remove not only fine particles but also radioactive particulates in air generated from nuclear power plants. The HEPA filter in the gas masks has corrugated HEPA filtering media instead of aluminum separators for ensuring air ventilation between filtering media.
Thus in the canister of the gas masks for the nuclear power plants, based on the three filter system, there is installed the pre-filter, the HEPA filter, and a filling of the impregnated activated carbon.
However, in the conventional gas mask manufacturing method, there are encountered the following problems. That is, when installing the filtering material into the canister, the sealing is usually imperfect, with the result that leakages occur frequently, and that the filtering material is frequently damaged. Further during the filling of the impregnated activated carbon particles, the filling becomes non-uniform, with the result that the adsorption efficiency for the radioactive gas is lowered. Further, due to the difference in the pressure losses, the respirations become irregular.
Therefore, in the above described manufacturing method, the manufacturing efficiency is low, the product defects are high, and the whole filter has to be discarded when a defect occurs. Further, the canister of the conventional gas mask is impossible to reuse, thereby adding to the volume of radioactive waste. Further, after each use, the contaminated radioactive materials on the outside of the canister have to be removed by decontamination methods.